Low molecular weight alpha olefins can be synthesised by polymerisation of ethylene. It is known in the art that this process produces even carbon numbered olefins having 4 to 50 carbon atoms and terminal double bonds. In some cases branched olefins are also produced.
Present commercial processes for making C4 to C20 linear alpha olefins are based on Ziegler high pressure growth reaction on aluminum triethyl (Ethyl process, U.S. Pat. No. 3,906,053, 1975) followed by low pressure displacement or non-Ziegler route. The Gulf process uses a one step catalytic reaction, wherein chain growth and elimination occur simultaneously in the same reactor (DE 1443927, 1961). In the non-Ziegler route, organo-nickel complexes in combination with a modifier is employed for SHOP process (U.S. Pat. No. 3,676,523, 1972; U.S. Pat. No. 3,726,938, 1973; U.S. Pat. No. 3,825,615, 1974; European Patent 177999, 1986). ZrCl4-EtAl2Cl3-Thiophene catalyst has been employed in the Idemitsu process (European Patent 241956, 1987; Japanese Patent 6259225, 1987).
The use of Ti(OR)4 (R=Cresyl)-EtAl2Cl3-PPh3 to obtain better control over distribution of alpha olefins is described in Indian Patent 182153 (1999) and in European Patent 0722922 (1999). The Exxon process (U.S. Pat. No. 4,409,414, 1983 and U.S. Pat. No. 4,486,615, 1984) has shown that at least 90 mole % linear alpha olefins having average molecular weight ranging from 70 to 700 can be obtained from oligomerising ethylene in the presence of AlEt2Cl—AlEtCl2—TiCl4-t-BuOH and AlEt2Cl—AlEtCl2—ZrCl4-n-BuOH catalyst systems.
UOP has developed a process for oligomerization of ethylene using nickel based catalyst in sulfolane solvent (U.S. Pat. No. 4,689,437, 1987). The purity and distribution of alpha olefins are increased by adding 1 to 6 wt % water as an additive.
However, the prior art processes suffered from several disadvantages. For example, the UOP process mentioned above employ very high ethylene pressures, in the range of 95 to 140 atmospheres. Also in this process, the conversion of ethylene drops sharply from 57.8% (0.71% water additive) to 11.3% (4.51% water additive) after 4th reaction time. In the Idimetsu process mentioned above, other polymers, apart from alpha olefins are formed. The prior art catalysts system also suffer from a higher deactivation rate.
Therefore, there is an urgent need for an improved process for the preparation of linear low molecular weight alpha olefins in high yields, which also avoids the above-mentioned drawbacks of the prior art. There is also an urgent need to provide a catalyst system, which has a much lower deactivation rate as compared to the prior art catalysts.